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Pregnancy and weight gain

We explore the recommendations for weight gain during pregnancy. By Kirsten Braun

Pregnancy is often a time when women feel they can be more relaxed about their weight. Who hasn’t heard the saying ‘you’re eating for two now’? Many women are confused or simply unaware of how much weight they should gain during pregnancy. Research suggests that women who are overweight or obese are more likely to overestimate the appropriate amount of weight gained during pregnancy.

While Australia does not have any official guidelines on weight gain during pregnancy, the Institute of Medicine (IOM) guidelines have been widely adopted. The IOM recommendations for weight gain during pregnancy are based on a woman’s pre-pregnancy body mass index (BMI). A woman’s BMI is calculated by dividing the woman’s weight in kilograms (kg) by the square of their height in metres (m). For example, a woman who weighs 75 kg and is 1.70 m high will have a BMI of 25.95 (75÷(1.7x1.7)=25.95).

The following guidelines apply to women with uncomplicated pregnancies of one baby.

Recommended weight gain during pregnancy

Pre-pregnancy BMI

Total weight gain range (kg)

Rates of weight gain for second and third trimester (average range in kg/week)

Underweight (<18.5)

12.5-18

0.51 (0.44-0.58)

Healthy weight (18.5-24.9)

11.5-16

0.42 (0.35-0.50)

Overweight (25-29.9)

7-11.5

0.28 (0.23-0.33)

Obese (≥30.0)

5-9

0.22 (0.17-0.27)

What the table means

Women who are underweight pre-pregnancy are advised to put on the most weight to ensure the proper nourishment of the baby. Conversely, women who are overweight or obese are advised to put on a much smaller amount of weight.

The table also spells out the amount of weight that should be gained per week for the second and third trimester. An amount of weight gain is not included for the first trimester as it is not expected that women should gain weight during this trimester. This is also in keeping with the guidelines around extra kilojoule consumption – women do not need to increase their kilojoule intake until the second and third trimester.

What is the weight gain made up of?

If an average new baby weighs approximately 3,300 grams (g) when it is born, what is the extra weight due to? The weight that women put on during pregnancy comes from a number of different areas, including:

actual weight of the baby (on average 3,300 g)

placenta

amniotic fluid

additional uterine tissue

additional breast tissue

fat stores

increased amount of blood

How much weight do women typically gain?

In Australia, approximately 50% of women who become pregnant are either overweight or obese. One study showed that while 36% of women gained weight according to the IOM guidelines, a further 38% of women gained excess weight. Interestingly, not gaining enough weight was also an issue with 26% of women gaining inadequate weight. Women who were overweight were the most likely group to gain excess weight, with 56% gaining more than the guidelines.

What are the health consequences of inadequate weight gain?

While the focus is often on women gaining too much weight during pregnancy, there are also health issues for inadequate weight gain. Inadequate weight gain is linked to premature birth, having a baby of low birth weight and a higher risk of the baby dying in the first year. For many women, morning sickness can impact on the ability to put on enough weight. Women should not be overly concerned if they don’t put on weight in their first trimester or even if they lose some weight. If, however, they are not gaining weight by their second trimester they should contact their health professional.

What are the health consequences of excess weight gain for mums?

If a woman is overweight or obese during pregnancy it increases the risks of complications like miscarriage, stillbirth, high blood pressure, pre-eclampsia, blood clots, gestational diabetes and having a large baby. These women are more likely to have their labour induced, have a prolonged labour, have their baby’s shoulder become stuck during delivery (shoulder dystocia), have an instrumental delivery (use of forceps, vacuum), have a Caesarean section or heavy bleeding after delivery. The excess weight can also make it more difficult to have an epidural for pain relief as it is more difficult to insert the epidural needle correctly. Women who gain too much weight during pregnancy will also experience more difficulty in losing the weight after their baby is born. Retaining this weight increases a woman’s risk of a range of health problems including cardiovascular disease and diabetes.

What are the health consequences of excess weight gain for babies?

Babies born to mums who gain too much weight during pregnancy have an increased risk of birth defects, premature birth and stillbirth. In addition, babies born to women who have gestational diabetes have a higher risk of developing Type 2 diabetes themselves later in life.

What you can do

Don’t ‘eat for two’ in the first trimester. Women who are of normal weight or above do not need to eat any extra kilojoules in the first trimester. In the second and third trimester women of a healthy weight only need to eat an additional 1,400 kilojoules (kJ)/day and 1,900 kJ/day respectively. This amount is even less for women who are overweight or obese.

Watch your serving sizes. A portion of lean meat, for example, is the size of your palm and a serve of pasta is half a cup of cooked pasta.

Participate in regular exercise. At least half an hour of moderate intensity physical activity on most, preferably all days. Pregnant women who have not participated in regular exercise previously, should consult with their general practitioner before starting an exercise program.

Are you a new mother who is struggling to lose her baby weight? Our updatedLooking After You booklet provides mothers with information and tips on how to achieve healthy eating and regular physical activity. Call 3216 0976 or 1800 017 676 (toll free outside Brisbane) for your free copy.